Impedance matching network and multidimensional electromagnetic field coil for a transponder interrogator

A method for interrogating a transponder for an inductively coupled identification system, said method comprising the steps of:

• providing at least two coils for generating a corresponding magnetic field component for each of said at least two coils, wherein said corresponding magnetic field components form a composite magnetic field having a varying phase and substantially constant amplitude;
• driving said at least two coils with at least one signal to generate said composite magnetic field, wherein each one of said coils generates said corresponding magnetic field component offset in phase by a certain degree relative to said corresponding magnetic field component of an adjacent said coil;
• aligning said at least two coils relative to each other and relative to said degree of offset in phase of said corresponding magnetic field components, to provide proper orientation of said composite magnetic field;
• detecting a transponder signal modulated on said composite magnetic field;
• and
• processing said transponder signal.

An emitter for an inductive coupling device, comprising:

• a driver circuit;
• an inductor having first and second ends, said inductor adapted to generate a magnetic field;
• a capacitor having first and second ends, said first and second ends of said capacitor coupled to said first and second ends of said inductor, respectively;
• and
• a series drive capacitor having first and second ends, said second end of said series drive capacitor coupled to said first end of said inductor, said first end of said series drive capacitor adapted to couple to said driver circuit which energizes said inductor.

A method of providing an impedance matching network for a coil in an electrical device, comprising the steps of:

• providing a desired resonance frequency for a coil and a required load impedance;
• determining the required capacitance and inductance;
• determining a ratio of drive impedance to a resistance of said coil;
• and
• determining an approximate value for a capacitor in parallel with said coil and an approximate value for a drive capacitor in series with said capacitor and said coil.